The invention relates to a process and a device for operating a motor vehicle with a chassis having a spring suspension mechanism and a shock absorption mechanism.
Even now current motor vehicles have a large number of control mechanisms, which may be divided roughly into passive and active systems. The interaction of such systems is growing in importance because of the explosive development of data processing. Active or semi-active vehicle control systems are known which, linked electronically to engine and transmission management, control suspension and shock absorption mechanisms on the basis of vehicle- specific parameters and perform functions such as level regulation, anti-skid and antilock control of wheels, and variable shock absorber control (soft setting for comfort or hard as in sports vehicles).
In order to achieve a more compact and more cost-effective suspension and shock-absorption mechanism, DE 40 19 732 A1 even proposes blocking or hydraulically locking the shock absorption mechanism at a specific lateral acceleration value, thereby providing support of the sprung masses for travel on curves at lower system cost. However, the control parameters are determined for specific driving conditions, and so the question is asked whether a solution such as this satisfactorily meets the requirements to be set with respect to travel comfort and performance.
The object of this invention is to propose a process whereby the safety of the vehicle can be improved. A process advantageous from the viewpoint of production engineering for application of the process is also proposed.
This object is obtained in the claimed invention by locking the shock absorption mechanism, at least for individual wheels, when an acceleration signal outside normal driving is sensed.
It is claimed for the invention that the effect of oscillation buildup of a motor vehicle structure or body which occurs occasionally in extreme driving situations is prevented. This buildup effect may occur both during full brake application as a result of extreme negative acceleration (deceleration) and during extreme starting acceleration or load alternation (delay in acceleration or vice versa) and may cause dangerous reactions with motorcycles or relatively short vehicles.
This oscillation buildup effect is also harmful in collisions as well, such as a side crash of a motor vehicle. As a result of possibly high impact energy the vehicle may initially dip downward on the impact side, with the wheels accordingly deflecting the springs and storing kinetic energy. Such dipping, in which the vehicle also generally is displaced sideways by sliding of the wheels, is due to the fact that (for example, in collisions with another motor vehicle) the point of impact with the bumper of the colliding vehicle is lower than the center of gravity of the vehicle subjected to impact from the side. During the subsequent displacement of the body in the direction of impact the deflected wheels increase this displacement to a considerable degree, such displacement possibly being magnified by the restoring action of the roll stabilizer, and the vehicle may even overturn in the process. This unstable oscillation may understandably be even more intense if the vehicle is carrying a roof load, since the center of gravity of the vehicle affected is moved farther upward as a result.
It is claimed for the invention that the unstable oscillation effect described above is now eliminated, in that, when the crash signal generated by a conventional method by an impact sensor or acceleration sensor is applied, the spring suspension and/or shock absorption mechanism is locked. The energy stored, possibly in the spring suspension and shock absorption mechanism, is as if it were frozen and is no longer able to apply torque to the instantaneous centers of the chassis or to the rolling axis of the motor vehicle extending through the instantaneous centers. In addition, the lateral stability of the motor vehicle is increased by the locked shock absorbers on the side facing away from the direction of impact.
Experiments have shown that the overturning of a vehicle which may occur under unfavorable circumstances can be efficiently and reliably prevented by application of the process described.
Locking of the spring suspension and/or shock absorption mechanism can itself be accomplished with a chassis having metal springs (such as hydraulic compression springs) and hydraulic-action telescopic shock absorbers by a conventional method, by employing an electrically controllable valve so that the piston with throttling ports of the shock absorber is controlled so that these throttling ports are closed or almost closed when the valve is in one of its switch-controlled positions; the shock absorber is accordingly hydraulically locked or rigidified, a process which is undergone also by the springs kinematically controlled in parallel by switch.
The crash signal may by preference be derived from one or more crash sensors present, for example, if the vehicle is equipped with an air bag system.
Hence cost-effective use may be made of means already present in the motor vehicle as part of its design. All that has to be done is to connect these means to each other suitably.
The same assertion applies equally to a situation in which an antilocking brake system (ABS) is already installed in the vehicle. In this instance a signal may be derived from the ABS if full braking of the vehicle accompanied by suitable ABS control (brake pressure modulation as determined by the positive and negative wheel acceleration values during braking) occurs, optionally supported by a pressure signal from the braking unit (high pressure corresponds to sharp deceleration on a road surface affording good traction).
A separate acceleration sensor may also be used as an alternative or in addition for starting acceleration, but for braking deceleration as well.